Hello! Yes, for this jam anything 2d is allowed. Text based, Visual novels, 2D Platformers, pretty much anything you want to Enter as long as its in 2d is allowed!
Yes you are only allowed to start working at the start of the week. You'll get a topic to use as a base for your game, and however you interpret that topic, and where you take it is up to you. Ideally At the start of the week it would be fresh code, but i'd be lying if i said i never recycled 1 or 2 lines in my time.
once the jam starts you'll see a submit button on the Jam Page. from there you can create a game page for your game on itch.io and it will then be a part of the jam. if there are any problems or confusions, ill be more than happy to help with that.